NEW ZEALAND EXPORTS. LEAD.

New Zealander, Volume 1, Issue 7, 19 July 1845, Page 2

NEW ZEALAND EXPORTS. LEAD.

Since the discovery by Mr. Grayling of Lead, on the ridge extending from Cape Colville to Mercury Bay, the same valuable metal has been again found near Cape Colville. To enable enterprizing persons in their researches to know the ore, we consider some few observations on the metal will not be uninteresting. The Lead ore of commerce is termed Galena, and is a compound of lead and sulphur, forming sulphuret of lead. It occurs massive and chrystalized, chiefly in the older secondary rocks. Its primitive form is the cube, of which there are several modifications, and among them, the octoedron. Its colour is blackish gray, without any shade of red, and its powder is black. As a sulphuret of lead Galena, consists, in 100 parts, of 86| of metal, and 13f of sulphur. It often contains traces of silver, and sonetimes in such quantity, as to render it worth separating, which is effected by exposing the roasted sulphuret to the action of heat and air in shallow earthen dishes ; the lead becomes oxidized and converted into litharge, while the silver is left pure, in consequence of its power of resisting the influence of heat and air. The argentiferous Galena has, in general, all the external characters of pure Galena. The proportions of silver vary considerably; sometimes, one-fifth part of the ore has been silver; but whenever more than 5 per cent exists, there are several other metals also associated with it, especially sulphuret of antimony. It is considered profitable to extract the silver when there are two parts in a thousand of galenaThe lead mines in England are not so rich in silver, as those of the continent of Europe. In the south of France, near Carhaix, is a lead mine which has been working for nearly three hundred years, supplying annually about 500 tons of lead, out of which is obtained above lOOOlbs. of silver; and there are other mines still richer in Savoy. The galena mines at Namur, are abundant in silver, and those, of Saxony contain a galena, so rich in silver that the lead is almost overlooked. The reduction of galena, that is, the separation of the lead from the sulphur, is a very simple process The ore is picked, and after being broken and well washed, is roasted in a rtverberatory furnace, the temperature of which is not so high as to

fuse the metal, but merely to soften it. During this process, it is kept stirred, till sulphurous fumes no longer ascend, when the heat is increased, and the metal brought to a state of fusion : the lead thus reduced, sinks to the bottom and is run out into moulds forming what are termed pigs. lhe mines of Great Britain produce an annual supply of about 48,000 tons of smelted lead, the whole of which is obtained from q alena or the sulphuret of lead.